(1) Field of the Invention
The present invention relates to a sheet post-process apparatus, a movable stack tray of the post-process apparatus, and a sheet post-process method that are used to perform post-processing of a sheet of, for example, paper that is discharged from an image forming apparatus, such as a copier, printer, or a multifunctional peripheral (MFP) as a multifunctional device.
(2) Description of the Related Art
Sheets, such as paper sheets, printed by an MFP or the like are then discharged from an outlet of a post-process apparatus connected to the MFP or the like (finisher), to be stacked on a stack tray. The number of sheets to be printed is arbitrarily specified by an operator via an operation panel of the MFP or a computer. Thus the number of sheets to be stacked on the stack tray may be only one or two in some case and may be substantially large to make loading amount substantially large in another case.
Since the position of an outlet for printed sheets is fixed, the height of an upper surface of the stack tray (stack surface) from the sheet outlet (difference in level) varies depending on the number of the sheets that have been already stacked on the stack tray. When the difference in level is reduced in size, there occurs a risk that the sheets may not be properly stacked. Therefore, a copier that may perform recording on a large number of sheets is generally designed such that a stack tray is movable, and the height of the stack tray is automatically adjusted, so that sheets can be properly stacked at all times.
Accordingly, when printing is perform on a large number of sheets, the stack tray is moved substantially downward in order to maintain the difference in level of the upper surface of the printed sheet relative to the position of the sheet outlet.
Conventionally, in a case such as described above, the stack tray is remained unchanged even after a large number of printed sheets have been removed. Then, when printing is newly started, the stack tray moved substantially downward is moved to a predetermined upper position.
In such a case, the stack tray moves to the predetermined upper position after printing started, it takes a time to the extent of having the risk of causing a delay in subsequent printing.
Therefore, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2003-26366, there is known a sheet stacking device in which, for example, the time period until a stack tray moves upward to a predetermined upper position is predicted, and sheets are immediately discharged after the time period has elapsed, thereby to improve the work efficiency as much as possible.
However, even with the device as described above, since printing cannot be performed during the time period until the stack tray moves up to the predetermined position after printing has been instructed, the work efficiency cannot be improved so much.